How do I locate the rear wiring harness on a 91

How do I locate the rear wiring harness on a 91 S-10 blazer to install trailer lights The owners manual (pg 2-45) claims "the 5 wire harness is stored along the left rear trim panel. the spare tire is inside. Must I remove the plastic guard from around the fuel tank to get this. I can feel 3 metal conduits inside the frame but can't reach the end with the wire protruding from them.

Thank you

Steve Feldman 303 909-2410